The injection of oxygen for removal of impurities in metallurgical process is well known, for example U.S. Pat. No. 2,855,293 and U.S. Pat. No. 3,706,549. Also, several U.S. patents disclose ways of diluting the oxygen with another gas in order to minimize the amount of oxygen that reacts with the metal. Such patents include Fulton et al. U.S. Pat. No. 3,649,246 and Ramachandran's U.S. Pat. Nos. 3,594,155 and 3,666,439. These patents deal only with the problem of increasing the degree to which the injected oxygen reacts with carbon rather than the metal. None are concerned with how one might utilize a diluent to maintain optimum gas flowrate through a supersonic lance while independently controlling cooling of that lance, lance height above the bath, flowrate of oxygen to the process, depth of penetration of the gas jet into the bath, and maximizing life of the lance.
In the use of a supersonic oxygen lance for injection into a steel bath in an electric are steel making furnace, for example, it is very important to control the gas flowrate within a narrow optimal range that is dictated by the injection nozzle design. This is described in “EAF Optimization: A Review of Maintenance and Operating Practices Leading to Optimum EAF Performance”, a short course published by the Iron and Steel Society, Warrendale, Pa., Jun. 19, 2000. Lance operation is also described in “Operation of Subsonic and Supersonic Nozzles”, Anatoli Parnas, published by American Combustion Inc., August 1997, as an operating document for use by its customers.
It is often desirable to reduce the rate of oxygen injection to a process for several reasons, including 1) to prevent over heating of the injection lance, 2) to reduce the penetration depth of the oxygen jet into the bath, and 3) to limit the reaction rate of oxygen with a given reactant. In the art, the current method of accomplishing the stated goals is to increase the distance from the tip of the injection lance to the process bath, or to reduce the flowrate of oxygen. Reduction of oxygen flowrate below the optimum range, however, causes loss of cooling and change of exit gas flow patterns near the lance tip. This can damage the lance, causing premature failure. Backing the lance away from the process can reduce the quantity of oxygen that participates in the reaction, and can effect cooling of the lance, but jet penetration is reduced, thereby reducing process efficiency. In addition, oxygen utilization efficiency is also reduced. The object of the present invention is to obviate the stated problems and deficiencies by provision of a means to independently optimize oxygen flowrate and total gas flowrate through the water cooled lance.